Geotechnical Fundamentals - Soil Types PDF

GEOTECHNICAL FUNDAMENTALS UNIT 2 Soil Types 2.1.0 Introduction 2.2.0 Definitions of Key Terms 2.3.0 Soil Types 2.3.1 Particle Size and Shape 2.4.0 Soil Structure 2.4.1 Cohesionless Soils...

GEOTECHNICAL FUNDAMENTALS UNIT 2 Soil Types 2.1.0 Introduction 2.2.0 Definitions of Key Terms 2.3.0 Soil Types 2.3.1 Particle Size and Shape 2.4.0 Soil Structure 2.4.1 Cohesionless Soils 2.4.2 Cohesive Soils 2.4.3 Clay Minerals 2.4.3.1 Kaolinite 2.4.3.2 Illite 2.4.3.3 Montmorillonite 2.5.0 Clay Mineralogy 2.5.1 Clay Structure 2.6.0 Soil Microstructure 2.7.0 Questions and Practical Problems 2.8.0 Web Resources 2.9.0 References 2.10.0 Field Picture #1 2.11.0 Field Picture #2 Soil Types 1 2020-09-29  GEOTECHNICAL FUNDAMENTALS 2.1.0 INTRODUCTION The characteristics and behavior of soil vary based on the materials’ physical properties. Will the soil be suitable for use in a roadway embankment, culvert installation, and sewage lagoons etcetera? In order to assess the suitability of a material for a specific engineering application it is important to be able to categorize the soil. The soil type or category is based on particle size; however, where the soil particle-size is too small to be observed, an additional physical property, known as plasticity, is used as a criterion for evaluation. Plasticity is based on the consistency of a soil; the soil’s ability to deform. Soil properties are not always controlled by particle-size and plasticity. Studies have shown that soil structure and mineralogical composition, including the interaction with water, can also significantly influence the properties and behaviours of soils. Recognizing and understanding the influence of the various soil properties is vital for design and construction involving soils. This module will:  examine the major soil types and categories based on particle size and shape;  explain the difference and importance of clay-size and clay minerals;  highlight the importance of clay mineralogy related to the soil properties and  outline the various soil structures. In order to gain some familiarity with the terminology related to soil types review the definition of key terms. 2.2.0 DEFINITION OF KEY TERMS (ASTM 1992) All the material located above bedrock including mineral particles (sand and clay) and organic material; Sediments or other Soil unconsolidated accumulations of solid particles produced by the physical and chemical disintegration of rocks, and which may or may not contain organic matter. The arrangement and state of aggregation of soil particles in a soil Soil Structure mass. Coarse-grained Soils made up of gravel and/or sand. Fine-grained Soils made up of silt and/or clay. Fine-grained soil or the fine-grained portion of soil that can be made to Clay (Clay Soil) exhibit plasticity (putty-like properties) within a range of water contents, and that exhibits considerable strength when air-dried. Clay Size That portion of the soil finer than 0.002 mm (0.005mm in some cases). Soil Types 2 2020-09-29  GEOTECHNICAL FUNDAMENTALS A soil that when unconfined has considerable strength when air-dried Cohesive Soil and that has significant cohesion when submerged. A soil that when unconfined has little or no strength when air-dried and Cohesionless Soil that has little or no cohesion when submerged. Particles that are so small that the surface activity has an appreciable Collodial Particles influence on the properties of the aggregate. Parent Material Material from which a soil has been derived. The property of a soil or rock, which allows it to be deformed beyond Plasticity the point of recovery without cracking or appreciable volume change. Material passing a 0.075mm standard sieve that is non-plastic or very Silt slightly plastic and that exhibits little or no strength when air-dried. A soil, which lacks the properties of plasticity; where the plastic soil Non-Plastic would have a range of water contents over which it would exhibit plasticity and which, would retain it shape on drying. Geometrical aspects consisting of size, shape, arrangement, and Texture crystallinity of the component particles and of the related characteristics of voids. A common clay mineral having the general formula Al2 (Si2O5 )(OH 4 ) ; Kaolinite the primary constituent of kaolin. A significant rock-forming mineral being a main component of shales Illite and other argillaceous rocks. A group of clay minerals characterized by a weakly bonded sheet-like internal molecular structure; consisting of extremely finely divided Montmorillinite hydrous aluminum or magnesium silicates that swell on wetting, shrink on drying, and are subject to ion exchange. The property of a soil or rock pertaining to its susceptibility to decrease Compressibility in volume when subjected to load. The maximum stress that a material can resist without failing for any Strength given type of loading. Consistency The relative ease with which a soil can be deformed Flocculent An arrangement composed of flocs of soil particles instead of Structure individual soil particles. Loose, open-structured mass formed in a suspension by the Flocs aggregation of minute particles. Honeycomb An arrangement of soil particles having a comparatively loose, stable Structure structure resembling a honeycomb. Single-grained An arrangement composed of individual soil particles; characteristic Structure structure of coarse-grained soils. Dispersed Structure The structure created by the net repulsion of clay particles which leads to a face-to-face orientation of the clay particles Soil Types 3 2020-09-29  GEOTECHNICAL FUNDAMENTALS The property of a material that enables it to stiffen in a relatively short time on standing, but upon agitation or manipulation to change to a very Thixotropy soft consistency or to a fluid of high viscosity; the process being completely reversible. Sensitivity The effect of remolding on the consistency of a cohesive soil. The removal of soluble soil material and colloids by percolating water or Leaching the removal in solution of the more soluble materials by percolating or moving waters. Remolded Soil Soil that has had its natural structure modified by manipulation. Interstitial Occurring between the grains or in the pores in rock or soil. 2.3.0 SOIL TYPES Soil is all the material located above bedrock. It is grouped into four major categories or types: gravel, sand, silt and clay. These four categories are reduced to two groups termed coarse- grained soil and fine-grained soil. Coarse-grained soil includes gravel and sand, which have individual particles that are large enough to see without magnification. Clay and silt are termed fine-grained soil because of their small particle sizes, which are too small to see without enhancement. The accepted standard ranges for the classification of the major soil types is determined by various standard classification systems including the American Society for Testing and Materials (ASTM), the American Association of State Highway and Transportation Officials (AASHTO), and the United States Agricultural Department (USDA). The two most common particle-size classification systems are outlined in the following table: CLASSIFICATION PARTICLE GRAIN SIZE (mm) SYSTEM GRAVEL SAND SILT CLAY AASHTO 76.2 to 2 2 to 0.075 0.075 to 0.002